mineralogy and physical properties of the proposed gale crater

Mineralogy and Physical Properties of the Proposed Gale Crater MSL Field Site Jim Bell, Ryan Anderson, Ralph Milliken, Ken Edgett, ...

Outline • Orbital-scale perspective

- Color and Dustiness - Mineralogy - Thermal inertia

• Implications for sediment transport (then and now) • Relationship to potential MSL observations and hypotheses

and with thanks to colleagues on the MSL Landing Site Working Group

MRO/CTX Gale Crater Mosaic

(Anderson & Bell, 2010)

50 km

NASA/JPL/MSSS

General context...

Base map for overlays from a variety of remote sensing data sets...

MRO/MARCI Gale Crater Mosaic

(Bell et al., 2009)

NASA/JPL/MSSS

MARCI visible wavelength color composite

RGB=653, 546, 437 nm

Upper mound and surrounding highlands to the E, N, and W: Dusty

Much of crater floor and highlands S of the crater: Sandy/cleaner...

MGS/TES Dust Cover Index

(Ruff & Christensen, 2002)

Dusty Not

Upper mound and surrounding highlands to the E, N, and W: Dusty

Much of crater floor and highlands S of the crater: Sandy/cleaner...

MGS/MOLA Elevation

MOLA Team/NASA/GSFC/Google

~ 4 km difference

avg. slope ~5°

The dark wind streak coming out of Gale and spreading to the south (as well as the one coming out of the southern end of the crater north of Knobel) may demon-strate that sediment can indeed be transported up and out of these holes, even (apparently) in the present climate regime...

...or are they just areas of preferential dust removal?

Gale

Knobel

MGS/MOC NASA/JPL/MSSS

ODY/THEMIS Decorrelation Stretch

RGB = Bands 8,7,5

Mafic (Olivine-bearing) and generally more dust-free materials appear as pink/magenta

More Felsic materials appear as yellowish

Low inertia, dusty surfaces appear blue

(Hamilton et al., 2009) NASA/JPL/ASU (also Stockstill et al., 2007)

ODY/THEMIS Olivine basalt endmember map

(Also Pelkey & Jakosky, 2002; Pelkey et al., 2004; Stockstill et al., 2007) NASA/JPL/ASU

MGS/TES • Dark Material: Surface emissivity spectra are similar to Surface Type 1

• Mineral abundances consistent with ~65% ol+px+plag basalt, ~10% sulfate, and ~20% "high silica phases" (e.g., zeolite, amorphous Si, alkali glass)

• No TES smectite doublet: - outcrops too small? - abundances < 10-20%? - texture/particle size?

(Rogers & Bandfield, 2009)

High elevation and relatively high dustiness of upper mound prevent detailed THEMIS study...

MEx/OMEGA Mineral Index Images


50 km

Low Calcium Pyroxene

MEx/OMEGA Mineral Index Images


50 km

High Calcium Pyroxene → significant basaltic (sand?) component to lower mound...

MRO/CRISM FRT, HRL Images

(Milliken et al., 2010)

olivine (dunes); (Mg,Fe)2SiO4

(Fe, Mg) smectite clays; e.g., nontronite Fe2(Si,Al)4O10(OH)2 ·n(H2O)

sulfates (monohyd.) e.g., kieserite MgSO4•H2O; sulfates (polyhyd.)

sulfates & clays


MRO/CRISM Survey Mode Images (F. Seelos et al., 2007)

MRO/CRISM Survey Mode Images (F. Seelos et al., 2007)

Similar RGB composite as Milliken et al. (2010):

Red = Fe minerals (OLINDEX)

Green = Fe/Mg clay (D2300)

Blue = sulfates (SINDEX)

• CRISM survey mode view so far mostly points out the extensive "basaltic detritus" signature, even in sulfate/clay areas...

• Consistent with OMEGA data and MER "dirty evaporites" story in Meridiani?

How Much Clay, Sulfate, Ol, Px, ...?

•  Important to remember that there is a fundamental ambiguity between grain size and abundance in near-IR spectroscopy: –  An absorption band could be X% deep because there is a small

amount of relatively coarse-grained (10s-100s of microns) material, or a large amount of relatively fine-grained (submicron-10s of microns) material

–  Despite a number of admirable efforts, abundance estimates of clays, sulfates, etc. in and around the proposed MSL field sites are still strongly dependent upon model assumptions (grain size, presence/absence of spectrally-neutral phases, opt. const., etc.)

•  Whether alteration products are major components of these surfaces or minor (accessory) phases will likely require the MSL payload to determine!

CTX: MSSS/JPL/NASA

2 km Mound Skirting Unit Channel fill

•  The trough between the light-toned ridge and the rest of the mound shows the strongest CRISM phyllosilicate signature in Gale. (Milliken et al. 2010)

Mound Skirting Unit

CTX: MSSS/JPL/NASA

Mound Skirting Unit

•  The trough between the light-toned ridge and the rest of the mound shows the strongest CRISM phyllosilicate signature in Gale. (Milliken et al. 2010)

2 km Channel fill

2 km

olivine clays sulfates sulfates sulfates & clays

Erosion-resistant ridges occur in the sulfate-bearing unit...


These kinds of features are relatively common in Gale, both on the mound and along the traverse out of the ellipse...

from HiRISE PSP_001752_1750; NASA/JPL/Univ. Arizona

Former fractures; filled with harder "cementing" material, then host rock eroded away?

Current fractures?


Sulfates here too?

Clays here too?


An Inferred Stratigraphic Column for a Section of the Gale Mound

This part of the section would be the primary focus of study by MSL

ODY/THEMIS Thermal Inertia

(Fergason et al., 2006) (also Hobbs et al., 2010) NASA/JPL/ASU

ODY/THEMIS Thermal Inertia

(Fergason et al., 2006) NASA/JPL/ASU


Gale Unit Mapping

• thermal inertia • geomorphology • mineralogy

Lots more detail in Ryan Anderson's paper that just came out in the online Mars journal: http://dx.doi.org/doi:10.1555/mars.2010.0004

Updated from Thomson et al. (2007)

Science Traceability: Goals → Measurements → Instruments

Summary •  Some key observations about the Gale mound:

–  It has layers of interbedded phyllosilicates and sulfates •  Changing (but not simple) environmental and alteration conditions •  Fe/Mg clays and (to a lesser extent) Mg sulfates suggest moderate pH and

good biologic preservation potential...

–  Large and apparently cemented ridges •  Do these characterize the post-depositional alteration of mound materials?

–  Many km thickness of continuous (?) strata •  Exploration of the preserved stratigraphy of ancient Mars!

•  Enigmatic sediment transport processes—even today? •  While the lower mound is the primary target, the traverse also

offers opportunities for mineralogic and morphologic studies of aqueous/fluvial processes (Ryan's talk)

mineralogy and physical properties of the proposed gale crater

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